JPH01292371A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent image which is free from ground staining even if the surface state of a photosensitive body changes by detecting image density by an image density sensor and correcting the quantity of a light beam. CONSTITUTION:The photosensitive body 5 is driven clockwise and its surface is charged electrostatically in this case by an electrostatic charger 6 and irradiated with laser light from an optical unit 7 to form an electrostatic latent image on the photosensitive body 5. This latent image is visualized with toner when passing a developing unit 8 and the visual image is transferred to recording paper 2 conveyed to the photosensitive body 5 by a transfer charger 9 and fixed 10 on the recording paper 2. Then an optional image pattern is written on the photosensitive body 5 and then the image density sensor 14 reads the density of the surface of the photosensitive body 5 and the density of the image pattern part to correct the quantity of the laser light according to the ratio of their A/D-converted values. Thus, the excellent image is obtained.

Description

[Detailed description of the invention] Numbing point 1 The present invention provides a laser beam printer, a digital copying machine,
The present invention relates to an image forming apparatus such as a facsimile machine.

BACKGROUND ART In a conventional image forming apparatus such as a laser beam printer, a laser diode that generates a laser beam is set to generate a predetermined amount of light when the apparatus is powered on, and this state is maintained thereafter. For this reason, when the surface condition of the photoreceptor changes due to deterioration or the like, background stains occur on the image, which poses a problem in image quality.

A possible method for preventing this is to stabilize the image quality by correcting the amount of laser light. In this case, it is desirable to perform light intensity correction for each print, but this would require extra development on the photoreceptor for each print, increasing developer consumption and reducing the cleaning area of the photoreceptor. The burden will also increase.

For this reason, a method of correcting the light intensity every time a certain number of prints is considered is possible, but in this case, when there is a change in process conditions, such as due to replacement of a photoreceptor, the amount of light is corrected until the next light intensity correction is performed. The image will not be stable. For example, when performing light intensity correction every 10 sheets, if one sheet is printed after light intensity correction, and then the driver releases the cover and performs some work such as toner replenishment, the printing process conditions will change for the next print. There is a high possibility that it has changed significantly, and if printing is performed using the correction value before the cover is released according to the normal light intensity correction cycle, a problem of poor image quality will occur.

Purpose The present invention solves the above-mentioned problems in the prior art.
The invention of claim 2 or 3 aims to provide an image forming apparatus that does not cause background smear on the image even if the surface condition of the photoreceptor changes and has good image quality. This reduces the consumption of developer and reduces the burden on the cleaning section, and even if the process conditions change due to opening and closing of the cover of the device main body, images with good image quality can be obtained for a certain number of subsequent prints. The purpose is to provide a forming device.

In order to achieve the above object, an image forming apparatus according to claim 1 of the present invention is an image forming apparatus that forms an image by scanning a photoreceptor with a light beam corresponding to a written image, writing an image pattern on a photoreceptor, detecting a first density on the surface of the photoreceptor and a second density of the image pattern portion by an image density detection means, and corresponding to the relationship between the -W degree and the second density; Claim 2, wherein the amount of light of the light beam is corrected by
In addition to the above, the image forming apparatus according to the above includes a counting means for counting the number of sheets on which the image is formed, and the image forming apparatus controls an execution interval at which the light amount correction is performed by the counting means, The photoreceptor detection means detects the presence or absence of the photoreceptor, and when the photoreceptor detection means detects the absence of the photoreceptor, the light amount is corrected before forming the next image. The image forming apparatus according to claim 3 is characterized in that, in addition to the features of claim 1, the image forming apparatus further includes a counting means for counting the number of sheets on which the image is formed, and correcting the light amount by the counting means. An image forming apparatus that controls intervals, and includes an openable/closeable cover and a cover opening/closing detection means for detecting opening/closing of the cover, and when the cover opening/closing detecting means detects the open state of the cover, the following is performed. The present invention is characterized in that the light amount correction is performed before forming an image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 is a longitudinal sectional view of a laser printer as an example to which the present invention can be applied.

Recording paper 2 fed from one of the paper feed trays 1 by a paper feed roller 3 is conveyed to a drum-shaped photoreceptor 5, which is an example of a photoreceptor, with timing set by a pair of registration rollers 4. The photoconductor 5 is driven to rotate in a clockwise direction, and at this time, the surface of the photoconductor 5 is charged by a charging charger 6, which charges the photoconductor 5 with an electric charge. An electrostatic latent image is formed on the photoreceptor 5 by being irradiated with laser light.

This latent image is visualized by the toner when it passes through the developing device unit 8 section that forms the toner layer, and this visible image is transferred by the transfer charger 9 to the recording paper 2 conveyed to the photoreceptor 5, and then transferred. The visible image on the recorded paper is fixed by the fixing device 1.
Fixed by 0. Then, the recording paper 2 leaving the fixing device 210 is conveyed by a paper discharge roller 11 to a paper discharge system or a double-sided printing system. On the other hand, the cleaning unit 12 removes residual toner from the photoreceptor 5 after the visible image has been transferred. Reference numeral 13 is a main motor that drives the mechanical parts of the printer.

An image density sensor 14, which is an example of image density detection means, and a photoreceptor detection sensor 15, which is an example of photoreceptor detection means, which detects the presence or absence of the photoreceptor 5 are provided near the photoreceptor 5. In addition, the electrical equipment section 16 at the top of the printer includes a main CPU10I shown in FIG.
It has an optical writing device gate array (hereinafter referred to as "r gate array") 103, etc., and is equipped with an engine board 17 that performs print sequence control, and a controller board 18 that has an image processing section A.

Further, a cover (not shown) is provided on the front of the printer main body to allow maintenance of the machine and replacement of parts such as the photoreceptor 5.

A cover switch 19 (see FIG. 2), which is cover opening/closing detection means such as a photo sensor, is provided.

FIG. 2 is a block diagram of the control system of the laser printer of the embodiment.

The control system includes an image processing section A, a sequence control section B, a laser diode (hereinafter referred to as rLDJ) unit section C1, a high voltage power supply section, a sensor around the photoreceptor, and the like.

The image processing unit A converts data sent from a host computer or the like into raster data for exposing a photoreceptor to a laser beam. Is the sequence control unit a print sequence system that controls the image writing timing on the photoreceptor, paper transport timing, etc.? It has a main CPU 101 that performs wholesale and controls print operation sequences, and a processor CPU 102 that controls process control. The hardware that makes up the process control is the main CPtJ1 that controls the start timing of the process control.
01, a gate array 104 that performs light intensity control of the light beam, that is, light emission output control of the LD for optical writing, and modulation control, a processor CPU 102 that performs light intensity correction of the light beam, that is, correction of the LD light emission output, and correction of the developing bias, and an image density sensor. 14, and the LD unit section C, the process control consists of writing an arbitrary image pattern on the photoreceptor 5, and then writing the image density sensor 1 on the photoreceptor 5.
4 reads the density of the surface of the photoreceptor 5 and the density of the image pattern area as voltages Vp and Vt, respectively, and performs a function of correcting the amount of laser light based on the ratio of A/D converted values.

An example of a method for correcting laser light intensity is described below, including print sequence start, LD light emission output setting, LD light emission output adjustment using gate array 103, image pattern writing/density reading, calculation of LD light intensity correction value, and light intensity correction. 2, the error handling method for the detected density value, and the reset when the cover is released will be explained in sequence with reference to FIG.

In the print sequence, when image data for one page is sent to the image processing unit A from a host computer (not shown), a start command is issued to the sequence control unit B, and the printing operation is started.

First, the driving of the main motor 13 is started, and thereafter each print sequence is performed by comparing the count value of the print timing counter (CTIME) with the set value stored in the jROM.

The light emission output setting of the LD is performed after a predetermined time has elapsed from the start of the main motor 13 and after a predetermined time has elapsed from the time when image writing for one page has been completed.
Ul0I is set to signal LDPSTO=LOW. As a result, the gate array 103 sets the signal LDEXPO=LOW and starts setting the maximum LD ratio output value. Gate array 1
03, when this setting is completed, the signal LDEXPO=HIG
Let it be H. Next, the main CPU 101 receives the signal LDPST.
After seeing that O=HIGH, the LD ratio output minimum value setting start signal LDPST1=LOW is generated. As a result, the gate array 103 outputs the signal LDEXP1=LOW.
to start setting the minimum value, and when this is completed, the signal L
DEXP],=HIGH.

In addition, the signal LDPST1=LOW is the signal LDPST1=LOW.
It also serves as a process control start signal for 2.

Adjustment for setting the light emission output of the LD by the gate array 103 is performed as follows.

When the signal LDPSTO of the main CPU 101 becomes LOW, first the signal VIDEO of the gate array 103 becomes LOW.
W to turn on the LD, and further controls the optical writing device 7 to set the maximum value of the amount of light emitted from the LD necessary to correct changes in process characteristics due to fatigue of the photoreceptor 5. . (At this time, the D/A converter 104, ~D, 1 is set to ALL”L by the processor CPU 102.
By setting the D/A converter 10 to
No current flows through 4. ) The D/A converter 104 is
When 0 to D, 1=HIGH, the maximum current set to the D/A converter 104 flows into the operational amplifier 105-2.
The output becomes close to the LD power supply voltage VLD, and no current flows through the transistor 106-1, so no current flows even if the LD is turned on.

D/A converter 104-1, ~D7 AL L
As the countdown starts from "HIGH", the light emitting output of the LD increases as shown in FIG. 3, and the output voltage of the voltage follower 108 from the photodiode 107 decreases accordingly. is lower than the reference value of the comparator 109-2 (when the output of the comparator 109-2 becomes "HIGH", this is detected by the gate array 103 and the output of the D/A converter 104-1, ~D11 By stopping the countdown, the maximum value of the light emission output of the LD is set.

Next, the D/A converter 104-1, ~D11 is fixed to the count value, and the D/A converter 104-3, ~D, and l are set to A L "HIGH", and the D/A converter A L for D0 to D7 of 104-2
As a result, when the output voltage of the voltage follower 108 becomes lower than the reference voltage of the comparator 109-1, the output of the comparator 109-1 becomes "HIGH", and the D/
By stopping the countdown of the A converter 104-2, the minimum value of the light emission output of the LD is set. This corresponds to the light emission output required when the photoreceptor 5 is not fatigued.

Such adjustment operations are performed for each print.

Note that during the setting, the gate array 103 outputs the signal LDEXPO=LOW during the maximum value setting, and the signal LDEXP1=LOW during the minimum value setting.

The process control sequence for image pattern writing/density reading is performed as follows.

As mentioned above, the signal LDPS from the main CPU 101
When TI=LOW is input manually, M control is started.

First, in writing the image pattern, as shown in FIG. 4, the setting completion signal for the minimum LD output value LDEXP l =
When HIGH is received (Fig. 4 ■), the image pattern writing timing check counter for process control is counted up every 10 m5ec, and when this reaches an arbitrary value, image pattern writing starts (Fig. 4 ■). ). Thereafter, the LED of the image density sensor 14 is turned on (FIG. 4 - ).

The pattern modulation signal is a pattern write start signal PC from the processor CPU 102 to the gate array 103.
When FGT=LOW is sent, the gate array 10
Generated from 3. When the check counter reaches a predetermined value, the signal PCFGT becomes HIGH and the pattern writing ends.

Next, the image pattern is read using the DTP switch 110.
Depending on the settings, one of the following (a), (C), and (C) will be executed.

DIPBO=LOW If DIPB1=LOW (a
) If DIPBO=LO-old PBI=IIIGH)
If old PBO-HIGHDIPB1=LO- then (C) (a
) Timing: When it is determined that a certain time has elapsed after the LD's light emitting output was set, the density of the photoconductor section, which is the first density, is converted to voltage and reading is started (Fig. 4 ■)
. This is done at 6ss intervals. The voltage digital values are stored in each memory (VPBUF) for 8 consecutive points from the start of reading.
O-7) Calculate the average value and store it in another memory (VPAVEO). After reading the 8 points of the average photoreceptor output voltage, the average photoreceptor output voltage is subsequently checked (Fig. 4 ■) (in this example, the average photoreceptor output voltage is
．． When the voltage is 2.5 V or less eight times in a row, reading of the image pattern area density, which is the second density, is started (Fig. 4 -). To read the pattern section output voltage converted to voltage, read 8 points,
The average value is calculated and stored in memory (VTAVEO).

Timing 2) After a predetermined period of time has elapsed after finishing writing the image pattern, check the output voltage of the photoreceptor at intervals of 6 m5ec (Fig. 4), and sequentially read each memory (VPBUFO
-31) Go to Hess door. If the number of read data is 3
When the value is 2 or more, the value of memory VPBUFn is changed to VPBUF.
Move to n-1 and store the latest data in the memory VPBUF31. When the voltage is 2.5V or less eight times in a row (Fig. 4 ■), VPBUFO-7 is used as the photoreceptor part output voltage, and the average value is stored in the memory VPAVEO, and VPBUF24-31 is outputted to the image pattern part. As a voltage, the average value is stored in the memory VTAVEO.

(C) Timing: After finishing writing the photoreceptor pattern,
After a predetermined time, read the photoconductor output voltage at 8 points, read the pattern section output voltage at 8 points after a predetermined time, and store the averages in the memories VPAVEO and VTAV.
EO hesdoor.

The correction value for the LD light amount is calculated by calculating VPAVE/VTAVE using the photoreceptor section output voltage VPAVE and image pattern section output voltage VTAVE obtained above, and then calculating the quotient (8
bit) (VDIVID). In other words, the base address of the LD light amount correction data table set in the ROM, the above VPAVE, VTAVE
The contents of the memory addressed as an offset are LD
This becomes a light amount correction value and is stored in the memory LDBIAS. As the base address, a correction data table is prepared for each pixel density, and the base address is changed depending on the pixel density information.

Incidentally, in the above, the ratio VPAVE/V of the output voltage of the photoreceptor part which is the first density and the output voltage of the image pattern part which is the second density is
Although the light amount correction is performed in response to TAVE, it is also possible to perform the light amount correction by other methods, such as by making it correspond to the difference in re-output voltage, for example.

The execution and timing of process control, which is execution of light amount correction, is controlled as follows.

In this embodiment, light amount correction is performed based on the number of prints. The count of the number of prints is determined by the number of times the image write signal FGATE output from the gate array 103 becomes active (CFGATE is counted up). Note that FGATE becomes active once for each printed page.

First, for the -th sheet, that is, CFGATE=O, as shown in FIG. Figure 11). That is, as soon as the correction value is obtained, the correction value is output.

Next, on the 10) Jth sheet (CFGATE=10 attached), the process control pattern is written in the
(arbitrary number), then MXN and (MXN+1)
)-th sheet (M=1.2.3.4-,). If the image writing signal is on (FGATE is LOW) at the time when the correction value is obtained,
The correction value is not output until it is turned off. In other words, except for the first time, the LD light intensity correction value based on the pattern written on the MXNth and (MXN+1)th sheets is reflected on the (MXN+2)th sheet. Figure 5*2). Also, if the image writing signal is turned off (FGATE is HI) when the correction value is obtained,
GH), the correction value is immediately output. That is, the LD light amount correction value based on the image pattern written on the MXNth image and the MxN+1th image is reflected on the (MXN+1)th image.

As mentioned above, if you do not perform light intensity correction for each print, but do it every certain number of prints, the number of light intensity corrections will be reduced.
As a result, it is possible to reduce the consumption of developer required for development performed for light amount correction, and the burden on the cleaning unit 12 that cleans the photoreceptor 5 after development is also reduced.

Error handling is performed as follows.

In this embodiment, the normal level range of the output voltage of the image density sensor 14 is VP between 2.5v and 4.5v, and VT
is between 0.2V and 2.0■.

Then, in any of the following cases, the error counter (ER
CNT) is incremented by 1, the error counter is set to 0 when it is normal, and when the value of this counter becomes 3, it is set as an error.

1. If the reading method is the above timing (a) 1) v
If the voltage does not go below the threshold level even after reading 32 times or more after completing 8 points of p reading, 2) V P A V E O < 2.5V or V PAVE O > 4.5 V or VTAVE < 0.2
If V or VTAVE>2.0V (7).

2. If the reading method is the above-mentioned timing 1) 62 times or more (0.37 seconds) after the start of reading the image density.
ec) If the voltage does not go below the threshold level even after reading, 2) V PAVE O < 2.5V or V PAVE O > 4.5 V or VTAVE < 0.2
V or VTAVE>2. In the case of O.V.

3. If the reading method is timing (C) above, V P
A V E O < 2.5V or VPAVEO>
4.5V or VTAVE<0.2V or HA TAVE
>2.0V17).

If the voltage value read in this way is outside the normal range, the following processing is performed.

1. If ERCNT=3, a process control error is displayed (LED, LCD, etc.), and the LD light intensity is set to the standard light intensity, that is, the initial state.

2.0<ERCNT<3 Process control error display (LED, !, C
D, etc.), and the LD light amount is the same as for the MXNth sheet.

By correcting the light amount using the method described above, it is possible to maintain a high quality image in the image forming apparatus, and at the same time, it is possible to speed up the correction of the LD light amount using software and simplify the hardware configuration.

Reset (initial setting) when the cover is released, etc. is performed as follows.

If the cover switch 19 detects that the cover is open for a predetermined period of time or longer, or if the photoconductor 5 is replaced, the detection signal of the photoconductor detection sensor 15 changes from ``No photoconductor''. If it changes to ``Photoreceptor present'', it will be reset at the start of the print sequence.This means that if the cover is opened and some maintenance work is performed, the printing process conditions may have changed. is large, or the deterioration of the photoconductor is resolved when the photoconductor is replaced.
If a normal light amount correction cycle is followed, good prints cannot be obtained until the timing of correction is reached, so the purpose is to reset and print with the light amount correction reflected from the first sheet.

According to the present invention as described above, in the invention of claim 1, the image density is detected by the image density detection means, and the surface state of the photoreceptor is changed by correcting the light amount of the light beam. In the invention according to claim 2 or 3, in addition to the above, by performing light intensity correction every time a certain number of prints are made, the number of light intensity corrections can be reduced and the development speed can be improved. In this case, when the process conditions change due to attaching or detaching the photoreceptor from the main body or opening or closing the main body cover to perform some work. In addition, by returning the light amount correction cycle to the initial state, the correction value is reflected in the print after the conditions have changed, and it is possible to obtain a good print.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a laser beam printer according to an embodiment of the present invention, Fig. 2 is a control block diagram thereof, Fig. 3 is a curve diagram showing a method for setting the light emitting output, and Fig. 4 is a timing diagram of its process control. FIG. 5 is an explanatory diagram of the process control generation and reflection method. 5... Photoreceptor 7... Optical unit (optical writing device) 14.
... Image density sensor (image density detection means) 15...
...Photoconductor detection sensor (photoconductor detection means) 19...
・Cover switch (cover open/close detection means) A...
・Image processing section B... Sequence control section C... Laser diode unit section LD...
... Laser diode 101 ... Main CPU 102 ... Process control CPU 103 ... Optical writing device gate array (and one other person) Fig. 3 LD Hirisuke 2 □ Fig. 4 ■ Fig. 5

Claims (3)

[Claims] (1) In an image forming apparatus that forms an image by scanning a photoreceptor with a light beam corresponding to a written image, an image pattern is written on the photoreceptor, and an image density detection means detects a first density on the surface of the photoreceptor. and a second density of the image pattern portion, and corrects the amount of light of the light beam in accordance with the relationship between the first density and the second density. (2) An image forming apparatus having a counting means for counting the number of sheets on which the image is to be formed, and controlling an execution interval for correcting the amount of light by the counting means, wherein the photoreceptor detects the presence or absence of the photoreceptor. 2. The image forming apparatus according to claim 1, further comprising a detection means, wherein when the photoreceptor detection means detects the absence of the photoreceptor, the light amount is corrected before forming the next image. Forming device. (3) An image forming apparatus having a counting means for counting the number of sheets on which the image is formed, and controlling an execution interval for correcting the light amount by the counting means, the image forming apparatus including a cover that can be opened and closed, and a cover that can be opened and closed. Claim 1, further comprising: a cover opening/closing detection means for detecting, and when the cover opening/closing detection means detects the open state of the cover, correction of the light amount is performed before forming the next image. The image forming apparatus described in .